It is not a factor of cluster being healthy. The general single-file idea works when there are no shards.
In a sharded setup, where a mutation runs across multiple groups of Alphas, then that mutation would be part of multiple WALs – each corresponding to that Alpha group. In that case, two mutations may interleave depending upon the order in which they ended up on the corresponding WAL.
In your above example, if color predicate is in a different group than animal predicate, then there are two different WALs involved. So, it is possible that blue < green in WAL1, while dog < cat in WAL2. So, the eventual result would be “green cat”.